1. Field of the Invention
The present invention relates generally to an inkjet printer, and more particularly to methods for determining the drying time of ink ejected onto a sheet of media and to inkjet printers using the same.
2. Description of the Related Art
In prior art, an inkjet printer forms an image on a sheet of media, such as paper, by positioning a printhead in close proximity with the recording medium, and selectively ejecting ink from a plurality of inkjet ting nozzles of the printhead to form a pattern of ink dots on the recording medium. During inkjet printing, the printhead is spaced apart from the recording medium in a plane perpendicular to the sheet of media. As the printhead is moved across the sheet of media, from one end to another in a scan direction, ink is selectively ejected from the inkjet ting nozzles to form a print swath. After completing at least one print swath, the sheet of media is indexed a selected amount in a sub scan, i.e., paper feed, direction.
A common problem is determining when the ink deposited on the media is dry so that smearing does not occur when the printed media is further processed in the imaging apparatus. The printout in FIG. 1 is a test page that was printed on an inkjet printer using default setting and duplexing using a common plain media, M. The printout contains regular and bolded text, a solid black block and a line of diamonds adjacent the left and right edges of the media M. The streaks S above the black rectangle are due to the ink not being fully dry (absorbed) when the paper underwent a duplex operation. In addition to these obvious streaks S, there is ink transfer T from the bold text as well which can be seen in the expanded portion of FIG. 1 shown in FIG. 2. A user would find this print output objectionable.
One cause for the smearing and transfer shown in FIGS. 1-2, is that some media absorb ink faster than others and the media M was moved prior to the ink being dry. In setting the default dry time, developers have to pick a value that seems to be the best balance between dry time and throughput. However, any users experiencing such smearing will view this dry time setting as unacceptable. Further, in our testing, plain media with the COLORLOK additive seem to have the most smearing. It is thought that the flocculation of pigment particles near the paper surface and the resulting “filter cake” impedes ink absorption by the media. Although there is a COLORLOK media setting in the printer driver software that doubles the dry time from about 10 sec to about 20 sec, many users will not appropriately change the setting resulting in smeared printed media. What is needed is a way for the inkjet printer to automatically determine when ink is sufficiently dried/absorbed so that further operations, such as a duplex operation, can be accomplished without smearing in the shortest amount of time.